I don't imagine the Gallente influence would have been at all subtle - I see it very much as a Berlin-esque situation, with very indentifiable cultural enclaves where the populations used to be forced to live in enforced segregation and, now that the walls have come down, there is only a slight blurring around the edges - along with the scars of the various conflicts still being visible.
The only cultural homogeneity would be in new construction in the urban centers - mostly cultural resource centers, economic centers and - most especially - administration centers for the new governments.
I'm kinda baffled how you could possibly have the idea that it would be a slow and peaceful intermeshing of cultures - given the cultural distinctiveness in the first place, the traditions of opression, the invasions, the segregations and the general antipathy that seem to be the bedrock of the situation. Perhaps I'm a little more at home to such concepts, given my childhood, growing up in British enclaves in Germany, Holland and Belgium, given Northern Ireland, given my time in Berlin.
Even before the invasions, the Gallente generally used their technology to settle in places that the Caldari had been unable to build cities. After the invasions, they bussed in colonial populations and enforced Caldari and Gallente districts even in the shared cities. Heth didn't create ghettos when he invaded, he simply enforced the existing ones - albeit with a heavier hand than the Gallente probably did and with the guards on the other side of the gates.